Antarctic Ozone Hole Hits 2013 Peak Size

Below:

Next story in Science

The Antarctic ozone hole reached its biggest extent for the year
on Sept. 26, 2013, the National Oceanic and Atmospheric
Administration announced yesterday.

At its maximum, the ozone hole over the South Pole measured a
whopping 7.3 million square miles (18.9 square kilometers),
making it almost twice the area of Europe. [ See
the ozone hole form over Antarctica ]

The ozone hole is a region of the stratosphere, the second layer
up in Earth's atmosphere, where the concentration of ozone, a
molecule made of three oxygen atoms, is less than 220 Dobson
units (a measure of the density of a gas in an entire column of
the atmosphere). The ozone layer, which stretches between 12
miles to 19 miles (20 to 30 km) above the Earth's surface,
provides the planet with an invaluable service: Ozone absorbs
ultraviolet light, which can help cause skin cancer and sunburn.
It is also the culprit behind damage to plants and plankton.

In the 1980s, scientists first detected a depletion of ozone
concentrations over Antarctica. The hole forms every year above
Antarctica
between September and November. The hole developed because of the
proliferation of chlorofluorocarbons (CFCs), chemicals that were
once widely used in refrigerants. In several chemical reactions,
CFCs bind to oxygen atoms, breaking ozone down into ordinary
oxygen molecules.

Through an international treaty called the Montreal Protocol
(first signed in 1987), 197 countries have agreed to phase out
the use of CFCs, and the ozone layer is gradually recovering. In
February, scientists reported that the
ozone hole reached a record low and was smaller than it had
been the entire previous decade. Scientists estimate the ozone
hole will be closed by the middle of the century.

The southernmost continent is particularly prone to ozone
depletion because the frigid winds circulating over Antarctica
make CFCs particularly good at stripping oxygen atoms away from
ozone molecules.

The ozone hole also has effects on climate, because it alters the
wind patterns over the icy continent, thereby altering cloud
cover and the levels of radiation that reach the Earth's surface
there.